This invention relates to a method and device of varying the axle orientation of camel-back suspension systems, in particular Mack tandem drive camel-back suspensions.
These types of camel-back suspension systems utilise rubber or polyurethane insulator blocks, which not only dampen the movement between the suspension and axle, but position and retain the axle relative to the chassis.
The Mack tandem drive camel-back suspension system is fitted to the majority of both onroad and offroad Mack trucked throughout the world, and is a proven and reliable rear end suspension system.
In recent years there has been a greater awareness of heavy vehicle operation on our roads, leading to increased road authority controls and tighter inspection and safety procedures. Also, the cost of operating heavy vehicles has increased rapidly. Fuel, tire and repair costs are now the major expense when running heavy vehicles.
The correct alignment of the wheel/axle assembly in relation to the vehicle chassis longitudinal centre line is a major factor in determining not only running costs of heavy vehicles, but the safety and driveability of such heavy vehicles. This is particularly true of the rear end of tandem drive camel-back suspension systems.
Any condition other than correct alignment of the rear end with the vehicle chassis longitudinal centre line can contribute to rear axle "steer". Misalignment of the drive/rear axle contributes to an off-thrust angle which, in order to maintain vehicle direction, must be offset by constant steering correction by the driver. This constant steering correction places the front steer tires at a "scrub" angle to the direction of movement, contributing to a rapid wear of the tires, particularly to the new generation radial construction tires. Similarly, the drive/rear tires are also running at an angle to the direction of movement of the truck and experience excessive wear. Therefore, all tires on the vehicle are being "scrubbed" thus experiencing rapid wear.
Recent investigations by Hunter Engineering U.S.A. revealed that an estimated 70% of heavy vehicles on the road are misaligned. This misalignment leads to rapid tire wear which is a major consideration contributing to increased fuel consumption. In fact, studies have shown that tire rolling resistance contributes over 42% to the overall vehicle energy consumption.
Clearly, there is a need for a simple and inexpensive method for varying axle orientation of camel-back suspension systems.
There have been, over the years, several methods of adjusting the drive/rear axle of heavy vehicles originally not fitted with any adjustment means, e.g., the Hendrickson beam system. The camel-back suspension system, in particular, can be adjusted using a one-eighth inch offset insulator block available from the original equipment manufacturer or several after market manufacturers. This insulator block is identical to the standard insulator block in that it comprises the rubber or polyurethane base and a pin which locates the insulator block in a leaf spring. However, the locating pin is placed at one-eighth inch offset from the centre line of the block. Any axle adjustment which is obtained from this offset insulator block is, however, very limited as there is no provision for any adjustment other than one-eighth of an inch fore and aft. Additionally the "upper block" in the paired arrangement is not offset the one eighth of an inch and is hence less effective in the offset obtained. In the vehicle alignment industry an offset of one eighth of an inch is not worthwhile particularly for heavy vehicles.
Other forms of adjustment include simply removing the locating pin of a standard insulator block and rewelding the locating pin in an appropriate offset location. Alternatively, the locating pin can be cut down on one side and rewelded on the other side so as to provide an appropriate offset.
These adjustment procedures are not only crude, but do not allow for any re-alignment or offset adjustment at a later date. The effect of the welding and resultant heat, severely affects the rubber bonding of the locating pin thereby contributing to premature block failure.
The prior art adjustment methods also do not allow for a wider incremental adjustment. Varying manufacturing techniques, increased production runs and a desire to lower the cost per unit with the widest variation of component tolerances possible, have all combined to create the need for an adjustment means of the critically positioned wheel/axle assemblies which can cope with these wider manufacturing tolerances, and yet improve axle alignment techniques.